In the installation of sewer pipes connecting residence or other commercial buildings with a central sewage system, such as a city sewer line, problems may develop in the sewer line that result in the sewer line becoming filled with sewage and waste water. These problems may be caused by the central sewer system stopping up and thereby backing into the sewer pipe between the residence and the sewer system. In this case, it is common for sewage to fill the pipes back into the residence, and to leak out on the floor of the building creating an undesirable and unsanitary situation.
It is common practice in plumbing construction to locate between the residence and the central sewage collection point a device known as a back water valve when the lowest plumbing fixture, in the residence or building facility, is lower than the upstream man hole cover. This back water valve is required to block backed up sewage from entering into the building through the sewage system. This device suffers from the deficiency that while it is supposed to block sewage being backed up, it sometimes traps solid material between its flapper and seal, which allows sewage to bypass and in turn allows the building to be flooded with sewage.
It is obvious then, that there is a need for a device which will block sewage backup, but will not interfere with, or trap, debris which is in the sewage.